1. Field of the Invention
The present invention relates to a photosensitive composition and, more particularly, to a photosensitive composition photosensitive to deep UV light.
The present invention also relates to a pattern formation method using the photosensitive composition.
2. Description of the Related Art
In the manufacture of various types of electronic parts requiring micropatterning such as a semiconductor integrated circuit, a photosensitive resin is widely used. Recently, high-density integration of electronic parts has been attempt as multifunctional, high-density electronic equipment has been used. Therefore, finer micropatterning is required.
In order to form such a fine pattern, a step-and-repeat reduction-projecting type mask aligner normally called a "stepper" is widely used as an exposure apparatus. Upon pattern exposure, this apparatus uses, e.g., g rays (wavelength=436 nm), h rays (wavelength=405 nm) and i rays (wavelength=365 nm) from a mercury lamp and XeF (wavelength=350 nm), XeCl (wavelength=308 nm), KrF (wavelength=248 nm), KrCl (wavelength=222 nm), ArF (wavelength=193 nm) and F.sub.2 (wavelength=157 nm) of an excimer laser. In order to form a fine pattern, the use of light having a short wavelength is preferred. Therefore, a demand has arisen for a resist having high sensitivity to deep UV light generated by an excimer laser or the like.
An example of a conventionally known photosensitive composition for an excimer laser is a photosensitive composition consisting of an acryl-based polymer such as polymethylmethacrylate (PMMA) or polyglutarmaleimide (PGMI) or a polymer having phenol, and an azide-based photosensitive reagent. A photosensitive composition containing the former polymer, however, has low photosensitivity to an excimer laser and a low dry etching resistance. A composition containing the latter polymer has high sensitivity to an excimer laser and dry etching resistance. Since, however, a sectional shape of a pattern formed by using this composition is an inverted triangle, it is difficult to control exposure and development.
In addition to the above problems, various problems arise in accordance with the type of light source used upon exposure as a minimum size is reduced. When exposure is performed by using light, for example, interference of reflected light caused by steps on a semiconductor substrate largely adversely affects a dimensional precision. When exposure is performed by using an electron beam, a ratio of a height to a width of a fine resist pattern cannot be increased since a proximitry effect is produced by backscattering of electrons.
As one of methods of solving the above problems, a multilayered resist system has been developed. In this system, a plurality of resist layers having different functions are stacked and sequentially patterned from an uppermost layer. In the system, each exposed layer functions as an etching mask for an underlying layer after development. This multilayered resist system is summarized in "Solid State Technology", 74 (1981), and many other studies of the system have been reported. A currently, generally attempted system is a three-layered resist system using upper, middle and lower layers. In this three-layered resist system, the lower layer functions to flatten steps present on the surface of an element and to prevent reflection of light on the element surface which is a cause of low resolution. The middle layer functions as an etching mask upon patterning of the lower layer, and the upper layer functions as a photosensitive layer.
By using the above three-layered resist system, finer patterning than that performed by using a single-layered resist system can be performed. The number of manufacturing steps, however, is increased to result in a cumbersome manufacturing process.